I edited my comment above with more thoughts and everyone is still posting, so I thought I would mention it lol. Maybe what I am thinking of as matte lines is something different than what they are. When I was scanning the SE trailer, the Millenium Falcon was flying away from the Deathstar and I saw lines around it. Is that a matte line?
I think what you’re thinking of is garbage mattes, which are boxes around the elements. These were never MEANT to be noticed and are very hard to see with proper contrast, but are nonetheless visible and part of the film.